A series of Cyclo-olefin copolymer (COC) blends were prepared via solution blending process and showed various miscibility because of different norbornene content as well as copolymer microstructure. Two kinds of nano-silica particles, including hydrophilic silica (Hp-SiO2) and hydrophobic silica (Hb-SiO2) were inducted into COC blends to deform the phase separation domains of COC blends. The properties and morphologies of the composites were characterized after preparation. The tensile moduli of 8007 blended films increase with increasing 5013 or 6013 content. The tensile moduli of the COCs composites slightly decrease either with 1 wt% Np- or Nb-SiO2. But the tensile strength and elongation increase as the 6013 content higher than 30 wt% in the 8007/6013 composites with 1 wt% Nb-SiO2 particles. By adding either Hp- or Hb-SiO2 particles, the haze value decreased in the immiscible blends (8007/5013) but slightly increase in the miscible blends (8007/6013). For all COCs and their blends, the transmittances are all higher than 85% with 1 wt% Nb-SiO2 loading. The phase separated domains deformed with nanosilica in 8007/5013 composites which might be a reason for lower haze. In addition, transparent composite materials can be manufactured from immiscible COC blends containing nanoparticles. (C) 2013 Elsevier B.V. All rights reserved.